What Does a Muddy Precipitate Indicate in a Redox Reaction?

[AikiGirl]

Homework Statement

"State what you would infer from each of the following observations and suggest experiments you would carry out to test the validity of your inferences: When an unpleasant smelling gas was bubbled into an orange solution of a substance 'A', a solid was formed and the mixture appeared muddy in colour. On warming with conc HCl, some of the solid dissolved and the solution appeared green in colour."

Homework Equations

This is what I came up with:
Possible gases: NH3, SO2, NO2, H2S, Cl2
Possible solns: Br2, (Cr2O7)2-, Fe3+

The Attempt at a Solution

The soln is either (Cr2O7)2- or Fe3+ because they both are reduced to a green soln.

So the gas should be oxidised.

NH3: (NH4)- (same oxidation state)
SO2: (SO3)2- (same oxidation state), (SO4)2- (no ppt),
NO2: (NO3)- (same oxidation state),
H2S: S (yellow ppt), SO2 (gas), (SO3)2-, (SO4)2- (no ppt),
Cl2: Cl- (mostly soluble)

That's what I can figure out, not sure if it's correct, and not sure where to go from here. Any help would be appreciated.

 

[Borek]

The soln is either (Cr2O7)2- or Fe3+ because they both are reduced to a green soln.

So the gas is a reducing one.

Note: gas can reduce the substance in solution, but the precipitate doesn't have to contain reduced form of the gas - it can as well contain gas in the form introduced (protonated/neutralized depending on circumstances).